I don't think you can. All LAN and WLAN IPs can access the interface. There is only the option to enable/disable remote (WAN) management.

I'd be inclined to try an ACCESS CONTROL policy under ADVANCED, which might give you control per device, not all WLAN, but I have doubts it will work for LAN websites, like the router Web interface is.

Your best option is to set a solid password for the admin account if you don't want wireless clients messing with it.

Well, as long as the user cannot connect to the WPA2 wireless, he doesn't have access to the http page for administration...

The other option will be to install DD-WRT on it...

But i am disapointed because my DIR-655 have the option to disable admin access on wireless, so Dlink just have to implement this option too on the DIR-615, this option should be default on all Dlink routers....